3. National Iranian Oil Co. - 6.4 million barrels per day

Iran has been forced to curtail oil production due to international sanctions, but remains a huge oil and gas producer. To skirt sanctions, Turkey and India have reportedly been paying for Iranian oil with gold. The Strait of Hormuz remains the world's most significant choke point for oil. Iran has threatened to close the Strait if attacked. (Note: 2012 working interest production volumes calculated by Wood Mackenzie reflects oil plus the energy equivalent in natural gas.)